title: Ultralow-loss silicon waveguide crossing using Bloch modes in index-engineered cascaded multimode-interference couplers.
abstract: We investigate the loss mechanism in three-moded multimode-interference couplers that are the building blocks of a compact and low-loss waveguide crossing structure. Broadband silicon waveguide crossing arrays with <0.01  dB insertion loss per crossing are proposed using cascaded multimode-interference couplers, where lateral subwavelength nanostructures are used to reduce the insertions loss. We design and fabricate a 101×101 waveguide crossing array with a pitch of 3.08 μm. Insertion loss of ∼0.02  dB per crossing and crosstalk <-40  dB at 1550 nm operating wavelength and a broad transmission spectrum ranging from 1520 to 1610 nm are experimentally demonstrated.
authors.forename: Yang
authors.initials: Y
authors.lastname: Zhang
authors.forename: Amir
authors.initials: A
authors.lastname: Hosseini
authors.forename: Xiaochuan
authors.initials: X
authors.lastname: Xu
authors.forename: David
authors.initials: D
authors.lastname: Kwong
authors.forename: Ray T
authors.initials: RT
authors.lastname: Chen